Washington Hospital and Alliance Imaging have installed the first state-of-the-art open PET/CT scanner in the Bay Area, providing patients with convenient access - Monday through Friday - to one of the most accurate imaging technologies available.

A PET (positron emission tomography) scan is a type of nuclear medicine imaging that helps doctors see how the cells, tissues and organs inside the body are functioning. A CT (computed tomography) scan is a type of X-ray procedure that uses a computer to combine numerous X-ray images to produce detailed, cross-sectional views of the internal organs and structures of the body. By combining these two technologies, PET/CT scanners provide physicians with a powerful diagnostic and treatment-management tool.

"The CT scan is a widely used imaging test that gives superb anatomic detail of even very small internal body structures," says radiologist Dr. Jason Cheng, Medical Director of the Medical Imaging Department at Washington Hospital. "CT scans produce multiple images of the body in 'slices' that are less than a millimeter in width - which is thinner than a credit card. Those images are fed into a computer to produce a three-dimensional picture of the organ or area of the body being examined."

CT scans alone, however, have limitations, Dr. Cheng notes.

"The CT scan shows only the size, location and relationship of various structures in the body," he explains. "It doesn't tell you much about the function, which is where the PET scan comes in. With a PET scan, we inject a glucose solution with a small amount of a radioactive 'tracer' material into a vein. The tracer travels through the body and is absorbed by the organs and tissues being studied, where it gives off energy that is detected by the PET scanner.

"The PET scanner actually measures the metabolic activity of tissues, which is important because diseases such as cancer often begin with functional changes at the cellular level," he continues. "Cancer cells tend to metabolize sugar more rapidly than normal cells, so the labeled glucose used in PET scans preferentially localizes in the abnormal tissues. This means we can detect even very small tumors - before they have a chance to grow and cause changes in the anatomical structure that would be considered abnormal in a CT scan."

The newly-launched Philips PET/CT system at Washington Hospital enables small lesions to be detected, helping to diagnose disease in its earliest stages. In addition, it improves image quality and performance, regardless of patient size. The Open View design also allows for increased patient comfort by reducing claustrophobia and patient anxiety.

The PET/CT scanner fuses the data from the PET scan with images from a CT scan. "This is huge advantage because it allows us to determine the precise location of any abnormal metabolic activity detected," Dr. Cheng says. "Knowing the exact location of metabolic activity also is important in helping to determine if the activity is truly abnormal, since some organs such as the bowel and kidneys do show activity normally."

In addition to aiding in the diagnosis of cancer, PET/CT scans also can be used to determine whether a cancer has spread in the body (metastasized) and to assess the effectiveness of radiation therapy and chemotherapy treatments.

"We can use PET/CT scans to help guide biopsies to ensure more accurate tissue sampling," Dr. Cheng says. "We also can monitor tumors during and after treatments to determine whether the tumor has shrunk, as well as to tell if any residual masses are persistent cancer or just scar tissue that would not require further treatment."

While PET/CT scans are most commonly used to detect and monitor treatment effectiveness for cancer, they also can be used for other applications.

"PET/CT scans can help evaluate brain abnormalities," Dr. Cheng explains. "For example, we can detect the metabolic patterns in the brain that are characteristic of Alzheimer's disease. For uncontrolled epileptic seizures, we can find the abnormal section of the brain that is causing the seizures by looking at the metabolic patterns in the brain between seizures."

Using a different type of tracer, PET/CT scans also have been used in the evaluation of coronary artery disease and to help determine if there is damaged -but not dead - heart muscle that may respond to treatment with bypass surgery or angioplasty.

Dr. Cheng notes that if your physician has referred you for a PET/CT scan, it is important to follow the doctor's instructions for preparing for the exam, including fasting prior to the exam. "Generally, you want to have a low blood sugar level before the test, so that the labeled glucose used in the test is absorbed properly," he says. "This can be especially complicated for people with uncontrolled diabetes. Also, in people who exercise heavily, glucose tends to end up in the muscles, so you should avoid exercising for 24 to 48 hours prior to a PET/CT scan."